Quantifying the impact of land cover change on groundwater recharge of Welmel watershed in the Genale-Dawa Basin using the WetSpass model

ABSTRACT

Quantifying the Impact of Land Cover Change on Groundwater Recharge of Welmel Watershed in the Genale-Dawa Basin Using the WetSpass Model.

This study assessed the impact of land use and land cover (LULC) change on groundwater recharge in the Welmel watershed of the Genale-Dawa Basin using the WetSpass model. Spatial data on land cover, soil texture, slope, topography, groundwater level, and long-term meteorological records were used as model inputs. Land cover maps for 1991, 2001, 2011, and 2021 together with 33 years (1987–2020) of daily meteorological data were applied to estimate long-term seasonal and annual groundwater recharge. Model inputs were prepared as 30 m resolution grid maps and calibrated using literature and expert knowledge to represent watershed conditions. The results show that the mean annual groundwater recharge decreased from 241.8 mm in 1991 to 221.1 mm in 2001, 195.1 mm in 2011, and 168.5 mm in 2021. These values correspond to 22.2, 20.3, 17.9, and 15.5% of the mean annual precipitation (1,087.5 mm), respectively. Seasonal analysis indicates that most recharge occurs during the Belg and Kiremt seasons. LULC analysis revealed significant forest reduction and expansion of agricultural land, settlements, bush land, and grassland, which increased surface runoff and reduced infiltration. Overall, mean annual groundwater recharge declined by about 6.7% between 1991 and 2021 that corresponds to 73.3 mm equivalent to 23.9 and 48.9 mm of the wet and dry season, respectively, occurred mainly due to deforestation and agricultural expansion. The findings provide important baseline information for sustainable water resource management and land use planning in the watershed.